The polymerization of cyclic olefins, either alone, or with copolymerizable monomers, particularly olefins, has been significantly advanced with the discovery of the effectiveness of metallocene catalysts for coordination polymerization. Crystalline homopolymers can be prepared from the use of stereorigid, chiral metallocenes that yield conformationally regular or stereospecific polymers. See, New Materials by Polymerization of Cyclic Olefins with Metallocene Catalysts, W. Kaminsky, Paper for METCON '93, Houston, Tex. May 26-28, 1993, p. 325-335. Copolymerization with .alpha.-olefins can result in elastomeric polymers due to disruption of the crystallinity caused by the olefin incorporation. See, U.S. Pat. No. 5,204,429.
More recently it has been discovered that by careful selection of the ligand structure of the metallocene catalysts, copolymers having crystalline attributes can be prepared by copolymerizing olefins with the cyclic olefins. U.S. Pat. NO. 5,324,801 describes a process for the preparation of cycloolefin copolymers having from 1 to 80% of at least one cyclic olefin comprising copolymerization with an acyclic olefin in the presence of sandwich structured metallocenes where the sandwiching ligands are connected or bridged so as to form a ring. Preferred copolymers are said to have incorporation ratios of 40:60 to 60:40 of the cyclic olefin to acyclic olefin. Using the sandwich metallocenes exhibiting C.sub.1 symmetry, with the preferred ligands being fluorenyl and cyclopentadienyl, copolymers of alternating sequence ethylene and either of norbornene or tetracycloclododecene were prepared having crystalline melting points of 235.degree. C. to 335.degree. C. and molar ratios ranging from 50:50 to 41:59, cyclic olefin to acyclic olefin. Due to transparency the polymers are said to be suitable as glass substitutes, and suitable in polymer alloys. Further product description appears in Cherdon, et al, Cycloolefin Copolymers: A New Class of Transparent Thermoplastics, Angew. Chem. 223, 121-133 (1994).
Since these crystalline and semi-crystalline copolymers of ethylene, .alpha.-olefins, and cyclic olefins exhibit uniquely interesting physical properties, alternative means of preparing them, with potential improvements in ease of catalyst synthesis, increased polymerization efficiencies, increased cyclic olefin incorporation efficiencies and differing copolymer product characteristics are of great interest. Accordingly work was done to develop catalyst systems different from those previously discovered to be capable of such copolymerization processes.